This invention relates to a method and apparatus for reducing fat, oil and grease (FOG) contaminants in a laundry wash solution to permit discharge of the wash solution into the sewer system. More particularly, the method and apparatus described herein utilizes pH dependent surfactant chemistry to present a laundry surfactant which is capable of removing impurities, including FOG, from a laundry wash solution and later being deactivated as a surfactant to release the potentially polluting impurities to permit discharge of the wash water into the sewer system.
Discharge of contaminants into city sewer systems presents a significant problem to commercial laundries and industries which generate large volumes of aqueous solutions containing fat, oil and grease (FOG) contaminants. To discharge wash solutions into city sewer systems the level of FOG in the water, as well as other contaminants, must be reduced so discharge compliance may be accomplished. In the case of laundry operations this problem is a substantial concern as large volumes of discharge water are generated containing a variety of impurities and large amounts of hydrocarbon contaminants. These contaminants are removed from the soiled fabrics during the wash process and become chemically associated with the surfactant utilized to hold the impurities in aqueous solution. Since the object of an effective surfactant is to efficiently hold otherwise hydrophobic impurities in aqueous solution, the separation of surfactant bound hydrocarbons and impurities from the spent wash water is complicated by the primary utility of the surfactant. Therefore, the stronger or more efficient the surfactant in removing and suspending hydrophobic compounds in aqueous solution, the more difficult is the later separation of the impurities from the wash water.
In achieving efficiency in removal of FOG from laundry, surfactants have been developed which generate an emulsion with the FOG during the wash process. These emulsions tends to interfere with later removal of other water contaminants from spent wash solution. Therefore the emulsions compound the problem of cleaning the laundry waste stream by not only presenting greater difficulty in removing FOG from the water, but also in generating a FOG emulsion which interferes with the removal of other contaminants such as lead and other heavy metals which also must be removed prior to sewer discharge of the spent wash solution.
Attempts to break the FOG emulsion created by modern surfactants have generally had poor success. In particular, hydromechanical processes relying upon gravity separation alone are inefficient and time consuming. Other hydromechanical separating methods, utilizing the centrifugal force of a swirl chamber to create high g-forces to thereby separate oil and water are generally inefficient due to the surfactant creating a FOG emulsion which retards formation of sufficient oil droplet size to allow formation of an oil layer for mechanical separation from the water component.
Therefore, in order to efficiently separate FOG from wash water and permit removal of other contaminants it is necessary, at the conclusion of the wash cycle, to inhibit or reverse the emulsification of the FOG components. This surfactant reversal reduces or eliminates the FOG emulsion in aqueous solution so the FOG may be removed from the water without the interference of the previously desired emulsifying qualities of the surfactant. The resulting effect is that the FOG components will then exhibit normal hydrophobic characteristics.
One such method of accomplishing this result is to employ a surfactant which first may be utilized as a traditional surfactant to solubilize hydrophobic agents and suspend them in water. The surfactant is then capable of modification so as to reduce or remove its surfactant ability and permit release of the previously suspended hydrophobic constituents from the emulsion formed with the surfactant. Such surfactant reversibility is exhibited by amine based surfactants which within an alkaline or high pH environment act as typical nonionic surfactants and exhibit detergent action. However, in an acidic environment these amine surfactants loose their detergent abilities and perform as deemulsifiers to break down the stable emulsions of FOG in wash water and allow the FOG to separate from the aqueous phase.
Conventional surfactants utilized in laundry operations consist of a carboxyl group core as with the alcohol ethoxylate or ethylene glycol based surfactants. The surfactants utilized in the present invention, however, make use of a cationic amino group as the active moiety with a nonionic polyethoxy chain or other suitable hydrocarbon chain including additional de-emulsifying moieties to yield compounds whose surface active properties and water solubility depend directly on the pH of the solution in which they are present. These compounds are known generally as polyethoxy amines and have long been known as a class of compounds and have recently received attention as alternative laundry surfactant.
In solutions of high alkalinity or high pH of approximately 10 pH units or higher these compounds exist in the free amine form and function as nonionic surfactants. These amine surfactants act as typical nonionic surfactants and exhibit the same detergent powers of other, more commonly used, surfactants in an alkaline media. Historically, the cost of utilizing polyethoxy amines as wash surfactants has held the disadvantage of higher costs than the generally used ethoxylate compounds. However, with the increased costs associated with post wash cycle cleanup of spent washing solutions taken into consideration the initial higher cost of the amine surfactant compound can offer a cost effective option when the costs of spent wash solution cleanup are considered. In addition, the greater detergency efficiency of the amine compounds as compared to more commonly used surfactants, when identical quantities as a percentage by weight are used in the manufacturing of laundry detergent, allows an additional consideration in offsetting their slightly higher costs to end commercial applications. The recommended level of amine surfactant is in the range of 5 to 10 percent of the wash compound formulation as opposed to quantities as high as 20 percent of some currently utilized surfactant products.
The separation of the FOG from a reversible surfactant appears initially as finely divided droplets which do not tend to immediately separate from the water phase. This is due to surfactant activity being directed, essentially, to the molecular characteristics of impurities that affect solubility. As a result, impurities are released as individual molecules or as small groups of electronically alike charged particles which must then form into larger bodies or groups before achieving a sufficient buoyant size within the solution or sufficient electronic repulsion to overcome the adhesion to the surrounding water molecules to allow gravitational separation from the solution.
This need for impurity coalescence presents an additional problem in the separation of impurities on a commercial scale. To achieve simple gravitational separation from the aqueous solution a substantial amount of time is required for sufficient grouping of impurities to occur to allow eventual separation by the specific gravity of the respective impurities from the water solution. As commercial laundry operations discharge large quantities of cleaning solutions which must undergo separation, time of separation, as well as cost, is a major consideration in developing efficient separation methods for impurity removal.
It is, therefore, a general object of the present invention to provide a method and apparatus which overcomes the separation difficulties with respect to the presence of FOG emulsions in wash water.
Another important objective of this invention is to provide a method for breaking emulsions of FOG and impurities in wash water and thereby remove emulsion interference with the separation of heavy metals and other impurities contained in the wash water.
Still another important objective of the invention is to provide an apparatus for breaking up FOG emulsions in wash water and permitting the fat, oil and grease droplets to coalesce into a layer which may be removed from the aqueous solution.
Another important objective of this invention is to provide a time and cost efficient method of separating FOG from wash water so that pollutant free discharge of the waste water into public sewer systems that meet or exceed ordinance limits may be accomplished.
Yet another important objective of the invention is to provide a method and apparatus for emulsion reversal which permits wash water surface quiescence and to allow FOG accumulation atop the water layer during a continuous flow process.
Still another important objective of the present invention is to provide a method of rapidly and efficiently changing the pH of large quantities of spent wash effluent while avoiding wide pH changes during the acid injection process and while providing sufficient acid mixing with the effluent.
Another important objective of the invention is to provide a continuous flow process which allows sufficient time to accommodate complete reversion of the FOG emulsion and allow sufficient time for optimum separation of the FOG from the wash effluent.
Furthermore, it is an important objective of this invention to provide a cost efficient method of cleaning fat, oil and grease containing wash water while retaining the substantial cleaning properties of efficacious detergents.
Other objects and advantages of the invention will become apparent from the specification, drawings and claims.